Implantable articles of various shapes have been used for some time in plastic surgery to fill space subcutaneously in order to provide a more normal or desirable profile to the exterior surface of that portion of a person's body. These implants have traditionally been made primarily of elastomeric materials, particularly silicone. These types of articles are effective for their primary purpose of filling space in order to provide the desired exterior body contours, however, they have various disadvantages including a propensity to migrate from their site of original implantation if not properly anchored or attached. The typical silicone space-filling implant intended for facial repair is a solid article made from non-porous or substantially non-porous silicone. They are most commonly used when appropriately shaped for the repair of chins, cheeks and zygomatic arches. See, for example, U.S. Pat. No. 4,344,191 to Wagner and U.S. Pat. No. 4,790,849 to Terino.
In addition to facial implants, space-filling implants of many various designs are also used in other areas of the body. In particular, implants of various designs and constructions have long been used for breast augmentation. These devices are most typically constructed from silicone envelopes containing a soft filling material such as silicone gels. Implants of this type are of hollow-core construction and are beyond the scope of the present invention.
Materials other than elastomers have also been used for facial space-filling implants, most notably porous expanded polytetrafluoroethylene (ePTFE). Materials of this type are made as taught by U.S. Pat. Nos. 3,953,566 and 4,187,390 to Gore. ePTFE is commonly used as an implantable material because it is highly inert and thus typically provokes little if any adverse reaction when implanted. It is frequently used for tubular vascular grafts, sheet materials for patching membranes and blood vessels, dental barriers and sutures. It is also sold as a facial implant available from W. L. Gore and Associates, Inc. Flagstaff Aria., as GORE SUBCUTANEOUS AUGMENTATION MATERIAL.TM. (S.A.M.).
U.S. Pat. No. 5,098,779 to Kranzler et al. and PCT Published Application WO 95/22359 to Sharber et al. describe ePTFE space filling implants wherein the relatively soft ePTFE is rendered carvable (for shaping by a surgeon) by either coating or impregnating the porous ePTFE with a resorbable material, or by laminating it with alternating layers of another material such as silicone or fluorinated ethylene propylene (FEP) in order to render it adequately stiff for carving.
An article entitled "The Use of Gore-Tex.RTM. E-PTFE Bonded to Silicone Rubber as an Alloplastic Implant Material" (Berman et al., LARYNGOSCOPE, Vo. 96, No. 5, May 1986) describes the evaluation of implanted composite sheets of ePTFE sheet material laminated to sheets of silicone. Another article entitled "Sheets, 3-D Strands, Trimensional (3-D) Shapes, and Sutures of Either Reinforced or Nonreinforced Expanded Polytetrafluoroethylene for Facial Soft-Tissue Suspension, Augmentation, and Reconstruction" (Lewis et al., Journal of Long-Term Effects of Medical Implants, 8(1):19-42(1998)) describes facial repair implants of ePTFE having various shapes.
Facial space-filling implants of the types described above typically have exterior surfaces which are virtually entirely non-porous (e.g., silicone implants) or alternatively are virtually entirely porous (e.g., conventional ePTFE implants). The implants with porous exterior surfaces allow tissue ingrowth into those porous surfaces if they offer adequately large void spaces, typically of about 8-10 microns or larger, preferably larger than about 20 microns and less preferably of about 50 microns or larger. Tissue ingrowth results in a stable implant which is unlikely to have any tendency to migrate from its site of original implantation. Conversely, implants having substantially non-porous surfaces, that is either completely non-porous or having pores of too small of a size to accommodate any appreciable amount of tissue ingrowth, require suturing to adjacent body tissue for the necessary anchoring. Inadequate suturing frequently allows the implant to migrate away from its intended location.
While the ingrowth of soft tissue into an implant having porous exterior surfaces is desirable for stability of location, it is possible to dissect the attached soft tissue if it should become necesssary to remove the implant for any reason. However, if hard tissue (e.g., bone) has grown into the void spaces of the porous implant, the implant can be extremely difficult to dissect free should its removal be necessary.